Composite perfluorohydrocarbon membranes, their preparation and use

ABSTRACT

Composite porous hydrophobic membranes are prepared by forming a perfluorohydrocarbon layer on the surface of a preformed porous polymeric substrate. The substrate can be formed from poly(aryl ether ketone) and a perfluorohydrocarbon layer can be chemically grafted to the surface of the substrate. The membranes can be utilized for a broad range of fluid separations, such as microfiltration, nanofiltration, ultrafiltration as membrane contactors for membrane distillation and for degassing and dewatering of fluids. The membranes can further contain a dense ultra-thin perfluorohydrocarbon layer superimposed on the porous poly(aryl ether ketone) substrate and can be utilized as membrane contactors or as gas separation membranes for natural gas treatment and gas dehydration.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/979,565, filed Dec. 28, 2010, granted as U.S. Pat. No. 9,610,547 onApr. 4, 2017, which is a divisional application of U.S. patentapplication Ser. No. 11/744,018 filed May 3, 2007, which claims thebenefit under 35 USC 119(e) of U.S. Provisional application No.60/797,521, filed on May 4, 2006, all of which are incorporated hereinby reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention was made with government support under Grant No.DE-FG02-05ER84250 awarded by the Department of Energy (DOE). Thegovernment has certain in the invention.

FIELD OF THE INVENTION

This invention generally relates to composite perfluorohydrocarbonmembranes, their preparation and their use.

BACKGROUND OF THE INVENTION

Porous polymeric membranes are well known in the art and are used widelyfor filtration and purification processes, such as filtration of wastewater, preparation of ultra pure water and in medical, pharmaceutical orfood applications, including removal of microorganisms, dialyses andprotein filtration. Porous polymeric membranes are used to separatecomponents of liquid mixtures by membrane distillation and as contactorsto facilitate dissolution of gases in liquids or to remove gases fromliquids, as membrane bioreactors, and numerous other applications wherethey serve as a generic phase separator, for example, as a batteryseparator. Composite polymeric membranes that consist of a denseseparation layer superimposed on porous support are used in gasseparations such as natural gas treatment, gas dehydration, and hydrogenrecovery from petrochemical and refinery streams. These compositemembranes can be further utilized for removal of gases from liquids andfor dehydration of liquids. While these membranes have found broadutility for a variety of purposes, they suffer from severaldisadvantages: broad and non uniform pore size distribution, limitedchemical, solvent and thermal resistance, and surface characteristics,in particular when non-wetting, oleophobic properties are required.Porous polyolefin membranes, such as polypropylene and polyethylenemembranes, are utilized for membrane and as membrane contactors topromote dissolution or removal of gases from liquids. However, thesemembranes frequently wet out by the liquid media which leads toreduction in mass transfer and an inferior performance. Porous membraneswith improved surface properties are thus required for continuous stableoperation of membrane contactors. Furthermore, commercial porouspolymeric membranes exhibit limited solvent resistance that limits thescope of their application. Low cost porous polymeric membranes withtailored surface characteristics, uniform pore size distribution,improved thermal stability and solvent resistance are thus still needed.

Poly(aryl ether ketone)s represent a class of semi-crystallineengineering thermoplastics with outstanding thermal properties andchemical resistance. One of the representative polymers in this class ispoly(ether ether ketone), PEEK, which has a reported continuous servicetemperature of approximately 250° C. PAEK polymers are virtuallyinsoluble in all common solvents at room temperature. These propertiesmake PAEK attractive materials for porous membrane preparation. However,application of PAEK polymers to fabrication of membranes has beenlimited owing to their intractability, which prevents the use ofconventional solvent-based methods of membrane casting. PAEK polymerscan be chemically modified to impart solubility, for example, bysulfonation. However, articles formed from such functionalized PAEKpolymers lose many of the desired properties. Bulk modification leads toa disruption in polymer chain crystallization and articles subsequentlyformer from such functionalized polymers loose solvent resistantproperties.

A number of methods to prepare porous PAEK membranes have been disclosedin the art. It is known to prepare porous PEEK membranes from solutionsof strong acids, such as concentrated sulfuric acid. However, PEEK canundergo sulfonation in the concentrated sulfuric acid media and thus canloose some of its desirable sought after properties. U.S. Pat. No.6,017,455 discloses preparation of non-sulfonated porous PEEK membranesfrom concentrated sulfuric acid solvents sufficiently diluted by waterto prevent sulfonation. The membranes are formed by casting PEEKsolution to form a film followed by coagulation in a concentratedsulfuric acid. This membrane preparation process is complicated andproduces large amounts of waste acid.

U.S. Pat. No. 5,997,741 discloses preparation of porous PEEK membranesby forming a solution of PEEK polymer in a concentrated sulfuric acid atthe temperature of 15° C. or lower to prevent sulfonation. The solutionis processed and cast at a sub ambient temperature, followed bycoagulation in water or in a concentrated sulfuric acid. Only dilutePEEK solutions can be formed in the concentrated sulfuric acid whichadversely affects film forming characteristics, the mechanicalcharacteristics, and the pore morphology of the thus formed porous PEEKmembranes.

U.S. Pat. Nos. 4,992,485 and 5,089,192 disclose preparation of PEEKmembranes from non-sulfonating acid solvents that include methanesulfonic acid and trifluoromethane sulfonic acid. European PatentSpecification EP 0737506 discloses preparation of improved polymericmembranes based on PEEK admixtures with polyethylene terephthalate. Themembranes are formed by the solution casting process from a methanesulfuric acid/sulfuric acid solvent mixture.

The acid based solvent systems for manufacturing of porous PEEKmembranes disclosed in the arm are highly corrosive, frequently toxicand generate substantial environmental and disposal problems. For theseand other reasons, the acid based casting processes have found limitedcommercial use.

An alternative to the acid based solvent system for PEEK membranepreparation involves the use of high boiling point solvents andplasticizers that dissolve PEEK polymer at elevated temperatures. U.S.Pat. Nos. 4,957,817 and 5,064,580, both issued to Dow Chemical Co.,disclose preparation of porous PEEK articles from its admixture withorganic polar solvents having a boiling point in the range of 191° C. to380° C., such as benzophenone and 1-chloronaphthalene, and organicplasticizers capable of dissolving at least 10 weight percent of PEEK,respectively. The final porous article is formed by removing the organicpolar solvents and/or plasticizers by dissolution into a low boilingtemperature solvent. U.S. Pat. No. 5,200,078 discloses preparation ofmicroporous PEEK membranes from its mixtures with plasticizers whereinthe membrane undergoes a drawing step prior to or after the plasticizeris removed by leaching. U.S. Pat. No. 5,227,101 issued to Dow ChemicalCo. discloses preparation of microporous membranes from poly(aryl etherketone) type polymer by forming a mixture of PEEK type polymer, a lowmelting point crystallizable polymer, and a plasticizer, heating theresulting mixture, extruding or casting the mixture into a membrane,quenching or coagulating, the membrane and leaching the pore formingcomponents. U.S. Pat. No. 5,205,968, issued to Dow Chemical Co.,discloses preparation of microporous membranes from a blend containing apoly(aryl ether ketone) type polymer, an amorphous polymer and asolvent.

M., F. Sonnenschein in the article entitled “Hollow fibermicrofiltration membranes from poly(ether ether ketone)”, published inthe Journal of Applied Polymer Science, Volume 72, pages 175-181, 1999,describes preparation of PEEK hollow fiber membranes by thermal phaseinversion process. The use of a leachable additive polymer, such aspolysulfone, is proposed to enhance membrane performance. Preparation ofporous PEEK membranes by coextrusion of PEEK with polysulfone polymersfollowed by the dissolution of the polysulfone polymer from theinterpenetrating network is disclosed in European Patent Application409416 A2.

It is also known in the art to prepare porous PEEK membranes from itsblends with a compatible poly(ether imide) polymer, PEI. Preparation ofsuch membranes is described by R. S. Dubrow and M. F. Froix in U.S. Pat.No. 4,721,732 and by R. H. Mehta et al. in an article entitled“Microporous membranes based on poly(ether ether ketone) via thermallyinduced phase separation”, published in the Journal of Membrane Science,Volume 107, pages 93-106, 1995. The porous structure of these PEEKmembranes is formed by leaching the poly(ether imide) component with anappropriate strong solvent such as dimethylformamide. However, asdescribed by Mehta et at., the quantitative removal of PEI component byleaching is essentially impossible which in turn can lead to an inferiormembrane performance.

Japan Kokai Tokkyo Koho 91273038 assigned to Sumitomo ElectricIndustries, Ltd., discloses preparation of porous PEEK membranes by anion track etching method.

M. L. Bailey et al, in U.S. Pat. No. 5,651,931 describe a sinteringprocess for the preparation of biocompatible filters, including PEEKfilters. The filters are formed from a PEEK powder of a pre-selectedaverage particle size by first pressing the powder into a “cake”followed by sintering in an oven or furnace. The process is limited topreparation of filters with a relatively large pore size and a broadpore size distribution and does not provide economic means of forminglarge membrane area fluid separation devices.

A process for preparation of porous PAEK articles that preserves thedesirable thermal and chemical characteristics of PAEK polymers has beenrecently disclosed in U.S. Pat. No. 6,887,408.

Perfluoropolymers exhibit superior chemical durability and thus aresought after materials for preparation of membranes. Porousperfluoropolymer membranes are utilized for variety of filtrationseparation applications while non-porous amorphous perfluorpolymres areutilized in gas and vapor separation applications and gas transfer.Commercial porous perfluoropolymer membranes are typically available ina relatively large pore size (above 0.1 micrometer) and suffer from abroad and non uniform pore size distribution that can limit their use asseparation membranes and as gas/liquid transfer membranes due to surfacewet out. Stand alone porous perfluoropolymer membranes tend to compactunder high cross membrane differential pressures due to a relatively lowmodulus and tensile strength of perfluoropolymers. An attempt to remedythese deficiencies was made by preparing composite perfluoropolymermembranes. U.S. Pat. No. 4,754,009 to Squire discloses a gas permeablematerial that contains passageways wherein the interior of thepassageways is formed by solution coating ofperfluoro-2,2-dimethyl-1,3-dioxole, U.S. Pat. No. 6,540,813 to J. K.Nelson et al. discloses preparation of composite membranes fromperfluoropolymers by depositing a thin non-occlusive layer offluoropolymer on the exterior surface of a porous support, U.S. Pat. No.5,876,604 to Nemser et al. discloses preparation of compositeperfluoro-2,2-dimethyl-dioxole membranes that can be useful in gastransfer to and from liquids.

U.S. Past Patent 5,051,114 to Nemser et al. discloses amorphous aperfluoro-2,2-dimethyl-1,3-dioxole based polymers that can be used forgas separation and gas enrichment applications. U.S. Pat. No. 6,406,517to D. L. Avery et al. discloses preparation of gas permeable membranesfrom blend of perfluoropolymers with non-fugitive, non-polymericfluorinated adjuvant. U.S. Pat. No. 6,544,316 to R. W. Baker et al.discloses gas separation membranes with selective layer formed fromfluorinated polymer resistant to plasticization by the organiccomponents in the gas mixture.

The prior art composite perfluoropolymer membranes are formed bydepositing a perfluoropolymer onto a porous support. The porous supportis typically formed from a conventional polymeric material such aspolysulfone or polyetherimide. These porous supports are notsufficiently chemically or thermally resistant and degrade in long termoperation. The perfluoropolymer is not attached chemically to the poroussupport and thus the perfluoropolymer layer can delaminate and themembrane can otherwise develop defects due to the differential thermalexpansion of coating and substrate materials and/or substrate swellingwhen subjected to contact with solvent media or condensable vapor.

Thus there are still remains a need in the art for composite porousperfluoropolymer membranes with a chemically resistant substrate and auniform narrow pore size distribution with pore diameter below 100 nm.

Poly(aryl ether ketone)s are high performance engineering polymers thatexhibit exceptional thermal and chemical characteristics and are thushighly sought after as porous substrates for composite membranepreparation. However, the properties that make PAEK polymers desirablealso make preparation of porous membranes difficult. Chemical resistanceof PAEK polymers makes the functional modification of the preformedporous article difficult and such functionalized porous PAEK articlesare unknown. Preparation of porous PAEK membranes with perfluorohydrocarbon layers is not known in the art.

A number of techniques have been used in the art to chemically modifythe surface of dense PEEK films to affect surface characteristics suchas friction, wettability, adsorption and adhesion, including celladhesion. O. Noiset, et al., have modified the PEEK film surface usingwet-chemistry technique by selectively reducing ketone groups to formhydroxyl groups and then covalently fixing hexamethylene diisocyanate byaddition onto the hydroxyl function (Journal of Polymer Science, Part A,Vol. 35, pages 3779-3790, 1997). C. Henneuse-Boxus, et al., havemodified PEEK film surfaces using photochemical routes (European polymerJournal, Vol. 37, pages 9-18, 2001). P. Laurens, et al., have modifiedPEEK surfaces with excimer laser radiation (Applied Surface Science,Vol. 138-139, pages 93-96, 1999). N. Franchina and T. McCarthy havemodified semi-crystalline PEEK films with carbonyl-selective reagents toinduce surface functionality (Macromolecules, Vol. 24, pages 3045-3049,1991). The surface modified films were robust and unaffected by avariety of solvents. In U.S. Pat. No. 5,260,415 I. David disclosedprocess for the crosslinking of polymers containing diaryl ketone groupsby heating the polymer with alcohol and or alkoxide is enhance chemicalresistance.

SUMMARY OF THE INVENTION

Commercially available highly hydrophobic membranes generally aremanufactured from perfluorohydrocarbon polymers such as Teflon™. Thesemembranes exhibit non-uniform broad pore size distribution thatadversely affects separation efficiency. A broad pore size distributioncan result in poor separation by allowing unwanted species to passthrough or can lead to a wet out by solvents in the case of membranecontactor applications.

Since most membrane separation applications that utilize hydrophobicmembranes require a porous structure of highly uniform pore size, thereis a need for highly hydrophobic porous membranes with an average poresize below 1 micron combined with a narrow pore size distribution. Aneed also exists for commercially scalable process for the preparationof chemically and thermally durable composite membranes such as PAEKbased membranes with functional perfluorohydrocarbon surface layer(s),including porous PAEK membranes and use thereof.

In one aspect, the invention is directed to a porous composite membranewith an average pore size below 1 micron comprising aperfluorohydrocarbon layer chemically grafted to a surface of a porouspolymeric substrate.

In a specific example of the invention, a composite membrane includes aperfluorohydrocarbon layer on a porous poly(aryl ether ketone)substrate.

The membranes of the invention preferably are highly hydrophobic porousmembranes with an average pore sire below 1 micron combined with uniformnarrow pore size distribution. The membranes of the invention arecomposite and are formed by grafting a thin perfluorohydrocarbon layeron a surface of a preformed porous polymeric substrate.

In specific examples, the porous polymeric substrate has an average poresize below 1 micron, preferably below 0.1 micron and a narrow pore sizedistribution, further described below.

The porous polymeric substrate has reactive surface functional groups toallow for a covalent attachment of functional perfluorohydrocarbons.

The functional perfluorohydrocarbons include polymers and oligomers witha molecular weight of below 10,000 Dalton. Examples ofperfluorohydrocarbons containing reactive functional groups includeFluoroPel PFC 601 AFA (containing silane reactive groups) and PFC504A/coE5 (containing epoxide groups), both commercially available fromCytonix Corporation. The porous polymeric substrates with surfacehydroxyl groups are particularly preferred for the preparation ofcomposite membranes. The hydroxyl group can be an integral part of thebackbone of the polymeric material, such as for example in a cellulosebased polymers, ethyl cellulose and regenerated cellulose. Alternativelythe hydroxyl groups can be formed by surface modification of thepreformed porous polymeric substrate. The surface modification can becarried out by physical or chemical means as well known in the art.Examples of surface hydroxyl group formation by physical methods includeplasma treatment and UV irradiation. Examples of surface hydroxyl groupformation by chemical means include ozonation and lithiation followed byhydrolyses. Preformed porous polymeric substrates that can befunctionalized with surface hydroxyl group by physical or chemical meansinclude substrates made from polysulfone, polyether sulfone, polyimides,polyethylene, polypropylene, poly (dimethyl phenylene oxide) (PPO),polybenzimidazole, polycarbonate, polyester, and the like. The mostpreferred porous substrates of this invention that provide forpreparation of super hydrophobic membranes with nanometer size pores andnarrow pore size distribution are formed from poly (aryl ether ketones),PAEK.

In another embodiment, the invention relates to preparing highlyhydrophobic PAEK membrane by reacting ketone groups in poly(aryl etherketone) with perfluorohydrocarbon oligomer or polymer containing primaryamino-functional groups, ˜NH₂.

In a further embodiment, the invention is directed to a method in whichthe surface of the porous PAEK membrane is functionalized with reactivegroups such as hydroxyl groups followed by attachment of functionalperfluorohydrocarbons.

In one examples, the surface of PAEK membrane is functionalized byreacting with a primary amine compound containing hydroxyl groupsthrough keto-imine group formation. In another example the surface ofPAEK membrane is functionalized by reducing ketone groups of poly (arylether ketone) to form hydroxyl groups. The functionalization can becarried out on a pre-formed shaped porous PAEK membrane, or on a surfaceof a non-porous precursor article that is then subjected to poreformation. In some embodiments the functionalization and pore formationcan be carried out simultaneously in a single step process. The hydroxylgroups are then reacted with perfluorohydrocarbon molecules containingfunctional groups capable of covalent bonding to the surface hydroxylgroups, such as epoxy, isocyanate, acid chloride, silane, triazine andthe like functional groups. In some embodiments the functionalized PAEKsurface can be reacted with extender groups that then in turn arereacted with functional perfluorohydrocarbon groups. The porous PEAKmembrane can be subject to modification throughout the porous structureor selectively at the surface of the porous article only.) The compositeporous PAEK membranes with perfluorohydrocarbon functional surface layercan be further coated with perfluoropolymers to form porous or denseultra-thin surface layers to further affect membrane separationcharacteristics.

In one preferred method the functionalized porous poly(aryl etherketone) substrate is prepared by a process comprising: a) forming ablend of poly(aryl ether ketone) polymer with a polyimide; b) forming ashaped article from the blend, for example by extrusion, casting ormolding; c) optionally annealing the shaped article; d) forming a porousstructure throughout the shaped article while simultaneouslyfunctionalizing the surface of the shaped article by bringing thearticle into contact with a primary amine to simultaneously decomposethe polyimide in the shaped article into low molecular weight fragmentsand to functionalize its surface and removing the low molecular weightfragments from the article. After washing and drying, the porouspoly(aryl ether ketone) substrate containing reactive surface groups isreacted with a functional perfluorohydrocarbon to form a membrane.

In another preferred method the porous poly(aryl ether ketone) membraneof this invention is prepared by a multi-step process by forming aporous PAEK substrate, functionalizing the surface of the substrate withreactive groups and then reacting these surface groups with a functionalperfluorohydrocarbon. The porous PAEK substrate can be formed by amethod comprising: a) forming a blend of poly(aryl ether ketone) typepolymer with a polyimide; b) forming a shaped article from the blend byextrusion, casting or molding; c) optionally anneal in the shapedarticle; d) bringing the shaped article into contact with a primaryamine to affect decomposition of the polyimide in the shaped articleinto low molecular weight fragments under conditions that do not causefunctionalization of the poly(aryl ether ketone) polymer with theprimary amine; e) removing the low molecular weight fragments from thearticle; and f) drying the porous poly(aryl ether ketone) article.

The porous PAEK substrate formed by the above described process can bethen functionalized in a subsequent step by reacting the poroussubstrate with a primary amine containing one or more target functionalgroups including polar groups, such as hydroxyl groups, ˜OH, aminogroups, ˜NH₂, ˜NHR, ˜NRR′ and the like. The surface of the porous PAEKsubstrate can be also functionalized to form ˜OH groups by reducingketone groups in the poly(aryl ether) polymer backbone. The membrane ofpresent invention is then prepared by reacting surface groups withperfluorohydrocarbon containing reactive functional groups, such asepoxy, isocyanate, acid chloride, triazine or silane groups, capable offorming covalent bonds with the reactive surface groups. The porous PAEKsubstrate can be subjected to modification by the primary amine reagentor selective surface reduction throughout the porous structure orselectively at the surface of the porous substrate only. Composite PAEKmembranes can be prepared by functionalizing the exterior surface of theporous PAEK substrate only.

Functional perfluorohydrocarbons include oligomers and polymers.Furthermore, they may include mixtures of functionalperfluorohydrocarbons with soluble perfluoropolymers. Mixtures offunctional oligomers with non-functional polymers can be furtherutilized. The molecular weight of oligomers can range from severalhundred to several thousand and can be as high as 10,000 Dalton.

According to a further embodiment of the present invention, the aboveobjectives and other objectives that are apparent to those skilled inthe art are achieved by a method for separating a fluid mixture into afraction enriched in a first component and a fraction depleted in thefirst component, comprising the step of contacting said fluid mixturewith a fluid separation membrane what; maintaining partial pressuredifferential across the membrane, the membrane having been formed by aprocess which includes forming a perfluoro hydrocarbon layer on thesurface of a porous poly(aryl ether ketone) membrane, whereby thefraction enriched in the first component and the fraction depleted inthe first component are generated by preferentially permeating a portionof the fluid mixture through the fluid separation membrane.

The invention has many advantages. For instance, it provides a simple,cost effective, and industrially feasible process for the preparation ofcomposite porous PAEK membranes, modified with a perfluorohydrocarbonsurface layer. The composite membranes exhibit improved uniform porestructure, are solvent resistant and can operate at high temperatures.The composite porous PAEK membranes disclosed herein can be utilized asfluid separation membranes, for instance as microfiltration,nanofiltration, ultrafiltration, gas separation, membrane distillationand as membrane contractors. PAEK membranes including a denseperfluorohydrocarbon layer superimposed on the porous PAEK support haveimproved gas/vapor separation characteristic and high chemicaldurability.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference, to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular method and device embodying the inventionare shown by way of illustration and not as a limitation of theinvention. The principles and features of this invention may be employedin various and numerous embodiments without departing from the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWING

Not applicable

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention generally relates to composite membranes, theirpreparation and their use.

In preferred embodiments, the membranes of the invention are highlyhydrophobic porous membranes with an average pore size below 1 microncombined with uniform narrow pore size distribution.

In specific examples, the porous polymeric substrate has an average poresize below 1 micron, preferably below 0.1 micron and a narrow pore sizedistribution, further described below.

The pore size distribution of the porous substrate of this invention hasa ratio the pore diameter of the 90th percentile of the smallest poresin the distribution to the diameter. of the 10th percentile of thesmallest pores less than or equal to 5. Preferably, the pore sizedistribution has a ratio of the pore diameter of the 90th percentile ofthe smallest pore size to the diameter of the 10th percentile of thesmallest pore size less than or equal to 3. Most preferably, the poresize distribution would have ratio of the diameter of the 90thpercentile of the smallest pore size to the diameter of the 10thpercentile of the smallest pore size less than or equal to 2.

Geometric Standard Deviation (GSD) can also be used, to, characterizepore size distribution, GSD calculations involve determining theeffective cutoff of pore diameter (ECD) at the point corresponding tothe cumulative pore number of the smallest diameter of less than 15.9%and the effective cutoff of pore diameter (ECD) at the pointcorresponding to the cumulative pore number of the smallest diameter ofless than 84.1%. GSD is equal to the square root of the ratio of the ECDof the 84.17 percentile to the ECD of the 15.9 percentile The GSD has anarrow pore size distribution when GSD is less than 2.5, more preferablyless than 1.8.

The membranes of the invention are composite membranes that are formedby grafting a thin perfluorohydrocarbon layer on a surface of apreformed porous polymeric substrate.

The perfluorohydrocarbon preferably forms a contiguous ultra-thinsurface layer that can be several hundred angstroms thick or less. Insome embodiments the perfluorohydrocarbon thrills a monolayer. Theporous substrate can be grafted by the perfluorohydrocarbon reagentthroughout the porous structure or selectively at the surface of theporous substrate only.

In one aspect, the invention relates to the reparation of compositehydrophobic porous polymeric membranes formed by grafting a thinperfluorohydrocarbon layer on a surface of a preformed porous polymericsubstrate.

The porous substrate is preferably formed from a poly(aryl ether ketone)polymer, including poly(ether ketone), poly (ether ether ketone) andpoly(ether ketone ketone), collectively referred to as poly(aryl etherketone), PAEK. The method of instant invention provides preparation ofporous PAEK membranes modified with perfluorohydrocarbon functionalsurface layer to form a composite membrane with improved chemicaldurability and separation performance. Composite porous PAEK membranescan be prepared with target perfluoro hydrocarbon surface layer formedthroughout the porous body of the membrane or the perfluoro hydrocarbonmodification can be limited to the surface of the porous membrane only.In one embodiment of this invention the porous PAEK membrane is formedfirst followed by the surface functionalization with perfluorohydrocarbon. In another embodiment this invention, a porous PAEKmembrane formed by functionalizing the surface of a non-porous PAEKarticle first followed by the formation of the internal porousstructure. In further embodiment of this invention a composite PAEKmembrane is prepared by forming an ultra-thin dense perfluoro polymerseparation layer on top of the porous PAEK membrane. The porous PAEKmembrane can be in the form of a flat sheet, a tube or a hollow fiber.Composite porous PAEK membranes of this invention can be used for abroad range of applications, including porous membranes for fluidseparations, such as microfiltration, nanofiltration, ultrafiltration,as gas separation membrane for natural gas treatment and as dehydration,as membrane bioreactors, and as membrane contactors for membranedistillation and degassing of fluids.

The preferred composite membranes of this invention are prepared byforming a perfluorohydrocarbon layer on top of a porous PAEK substrate.Preferably the perfluorohydrocarbon layer is chemically attached to thesubstrate. Perfluoropolymers with functional amino groups can beutilized to react with ketone groups in the backbone of poly(aryl etherketone) polymer.

In another embodiment of this invention the surface or the porous PAEKsubstrate functionalized with reactive groups such as hydroxyl groups oramino groups to which functional perfluorohydrocarbons are attached in asubsequent step. In one such example the surface of PAEK substrate isfunctionalized reacting with a primary amine compound containinghydroxyl groups through keto-imine group formation. In another examplethe surface of PAEK substrate is functionalized by reducing surfaceketone groups to form hydroxyl groups. The hydroxyl groups are thenreacted with perfluorohydrocarbon molecule containing functional groupscapable of covalent bonding to the surface hydroxyl groups, such asepoxy, isocyanate, acid chloride, silane, triazine and the likefunctional groups. In some embodiments the functionalized PAEK surfacecan be reacted with extender groups that then in turn are reacted withfunctional perfluorohydrocarbon groups. The porous PEAK membrane can besubject to modification throughout the porous structure or selectivelyat the surface of the porous article only. The functionalization can becarried out on a pre-formed shaped porous PAEK substrate, or on asurface of a non-porous precursor article that is then subjected to poreformation. In some embodiments the functionalization and pore formationcan be carried out simultaneously in a single step process.

Functionalized PAEK articles, their preparation and use are disclosed inU.S. Pat. No. 7,176,273, with the title “Functionalized Porous Poly(ArylEther Ketone) Materials and Their Use”, issued on Feb. 13, 2007, theteachings of which are incorporated herein by reference in theirentirety.

The preferred functionalized porous PAEK membranes of this invention aresemi-crystalline. Namely, a fraction of the poly(aryl ether ketone)polymer phase is crystalline and is not subject to modification. A highdegree of crystallinity is preferred since it imparts solvent resistanceand improves thermo-mechanical characteristics to the article. In someembodiments of this invention the degree of crystallinity is at least1%, preferably at least 25%, most preferably at least 40%. Whenpre-formed, shaped porous substrates are utilized to form thefunctionalized membranes of this invention, the porous substrate can beformed by any method known in the art.

The porous substrate is comprised of a poly(aryl ether ketone) or ablend of poly(aryl ether ketone)s of the following general formula:[—Ar′—CO—Ar″]_(n)

wherein Ar′ ad Ar″ are aromatic moieties, wherein at least one aromaticmoiety contains a diarylether or diarylthioether functional group whichis a part of the polymer backbone, and wherein n is integer from 20 to500.

Preferably, the poly(aryl ether ketone) is selected from thehomopolymers of the following repeat units:

The poly(aryl ether ketone)s typically have a weight average molecularweight in the range of 20,000 to 1,000,000 Daltons typically between30,000 to 500,000 Daltons.

The preferred poly(aryl ether ketone)s of this invention aresemi-crystalline, and are insoluble inorganic solvents at roomtemperature. The most preferred poly(aryl ether ketone) of thisinvention poly(ether ether ketone), PEEK, and poly(ether ketone), PEK,both manufacture by Victrex Corporation under the trade name of Victrex®and poly(ether ketone ketone), PEKK, manufactured by Oxford PerformanceMaterials under trade name OXPEKK®.

The preferred method of forming porous PAEK substrate is by meltprocessing. The preparation of porous poly(aryl ether ketone) substratetypically consists of the following steps:

1. Forming a blend of poly(aryl ether ketone) polymer a porogen by meltblending. The porogen is alternatively a diluent (a high boiling, lowmolecular weight liquid or solid), an intermediate molecular weightoligomer or a polymer;

2. Forming a shaped article from the blend by melt processing, i.e.extrusion, casting or molding;

3. Solidifying the shaped article by cooling;

4. Removing the porogen (the porogen is typically removed byextraction);

5. Drying the porous PAEK substrate.

Prior to the porogen removal or subsequent to porogen removal thesubstrate can be annealed to increase the degree of crystallinity of thePAEK phase. The term annealing as defined hereto refers to a processingstep or condition that leads to an increase in the degree ofcrystallinity of the PAEK phase. The annealing can take place duringsolidification step through control of the cooling rate. For example,the annealing can be carried out in line during extrusion step bycontrolling the cooling rate. Alternatively or in an addition theannealing can be carried out in a subsequent step after the article hasbeen formed by solidification. In the later case the solidified articlecan be placed in an oven or transported through a heating zone for aperiod of time sufficient to affect crystallization. The article can beannealed at a temperature from about 150° C. to about 33° C., preferablyfrom about 200° C. to about 310° C., most preferably from 230° C. toabout 300° C. to increase the crystallinity of PAEK phase prior to theremoval of the porogen.

The use of polymeric materials as porogens is generally preferred.Examples of polymeric porogens include polysulfones, such as poly(ethersulfone), poly(ether ether sulfone), biphenol based polysulfones andbisphenol. A based polysulfone, and polyimides. The most preferredpolymeric porogens are polyimides. Poly(aryl ether ketone) type polymersform compatible blends with polyimides, PI. Removal of the polyimidecomponent from such blend article by solvent extraction is, however,very difficult due to polymer chain entanglement. The polyimide can bequantitatively removed, however, by selective chemical decomposition ofthe polyimide phase to form the final porous article. This method ofporous PAEK material preparation is referred to as Reactive PorogenRemoval process, RPR.

Polyimides that form the compatible precursor blend with the poly(arylether ketone) polymers are defined as polymers containing

linkages and include aliphatic and aromatic polyimides, copolyimides andpolyimide block and graft copolymers, wherein the polyimide is definedas a molecule that contains at least two imide linkages. Additionalpolyimides include aromatic polyamide includes, polyhydrazine imides andpolyester imides.

Aromatic polyimides are particularly useful for the preparation ofporous articles of this invention. The preferred aromatic polyimides aredescribed by the following general formula:

where n is an integer from 2 to 5,000, and where

is independently

or mixtures thereof.

where m equals 0 to 4.

Z and Z′ are:

—H, —CH₃, —CH₂CH₃, —CH₂CH₂CH₃, iso-propyl, iso-butyl, tert-butyl, —Br,—Cl, —F, —NO₂, —CN

where —Ar₂— is independently

or mixtures thereof, where Ar₁ and m are defined as above.

where m is defined above.

The most preferred polyimides are poly(ether imide)s, PEI, of thefollowing formula:

and poly(ether imide) copolymers manufactured by the General ElectricCompany under the trade name of Ultem® 1000, Ultem® XH1010F, Ultem® 6050and Siltem® STM1500. The copolymers that contain dimethylsiloxanesulfide units are examples of representative copolymers. Anotherpreferred polyimide is Aurum® manufactured by Mitsui and distributed byDuPont Engineering Polymers.

The polyimides can be used as a single additive component or as amixture of polyimides. The polyimides typically have a weight averagemolecular weight in the range of 500 to 1,000,000 Daltons, preferablybetween 1,000 to 500,000 Daltons.

The formation of the poly(aryl ether ketone) blend with the polyimidecan be carried out by mixing components in a molten stage, such as bymelt compounding, and other methods conventionally employed in thepolymer compounding industry. A plasticizer can be optionally added toaid processing. The thus formed poly(aryl ether ketone)/polyimide blendsform compatible blend compositions. The compatible composition isdefined as capable of forming porous poly(aryl ether ketone) articleswith inter-connected pore structure and an average pore diameter of 10micrometer or less. Preferred compatible blends are PEEK/PEI blends thatform poly(aryl ether ketone) articles with inter-connected porestructure and an average pore diameter of 1 micrometer or less. The mostpreferred compatible blends are the PEEK/PEI blends that form poly(arylether ketone) articles with inter-connected pore structure and anaverage pore diameter of 100 nanometers or less. The applicationrequirements determine the desired pore size that in turn is determinedby the polyimide structure and by the processing conditions.

Blends suitable for preparation of porous articles in accordance withthis invention comprise from about 5 to about 95 weight percent of thepoly(aryl ether ketone) polymer component, preferably from about 20 toabout 75 weight percent of the poly(aryl ether ketone) component, mostpreferably from 40 to 60 weight percent.

The blends can contain various additives in addition to the compatiblepolyimide component, including solvents to reduce blend viscosity,stabilizers, flame retardants, pigments, fillers, such as catalyticparticles, plasticizers, and the like. Other polymers can be alsopresent in the blend to provide a desired additive property and inparticular to modify pore size. One such preferred additive polymer ispoly(ether sulfone).

The poly(aryl ether ketone)/polyimide blends can be fabricated into aflat sheet film, a fiber, a hollow fiber or other desired shapeprecursor substrate by melt extrusion, casting or molding. The articleconfiguration will depend on the intended use. Prior to polyimide phaseremoval the article is preferably annealed to increase the degree ofcrystallinity of the PAEK phase. As discussed above, the annealing cantake place during solidification step through control of the coolingrate.

The removal of the polyimide component of the blend can be effectivelycarried out by the RPR process utilizing reagents that decompose thepolyimide into low molecular weight easily extractable fragments. Thesuitable classes of reagents include but are not limited to ammonia,tetraalkylammonium hydroxides, hydrazine, alkylhydrazines,hydroxyalkylhydrazine, primary aliphatic amines, or secondary aliphaticamines. In some embodiments, the reagent that affects polyimidedecomposition is diluted with a solvent. Examples of suitable solventsinclude alcohols, ketones, hydrocarbons, water, and aprotic solventssuch as NMP, DMF, and the like. Reagents suitable to decompose thepolyimide phase in accordance with this invention include, but are notlimited to, ammonia, tetramethylammonium hydroxide, hydrazine,methylamine, ethylamine, propylamine, butylamine, ethylenediamine,propylenediamine, butylenediamine, morpholine, piperazine,monoethanoamine, ethylethanolamine, diethanolamine, propanolamine,diproponalamine, and mixtures thereof. Commercially available aminemixtures, such as Ucarsol®, can be also employed. The preferred aminesinclude hydrimine, monoethanolamine, tetramethylammonium hydroxide, andtheir mixtures with alcohols, such as methanol, ethanol, isopropanol,butanol, ketones, water, and aprotic solvents. The most preferredreagents for the decomposition of the polyitnide phase are themonoethanolamine and the tetramethylammonium hydroxide. Thedecomposition and removal of the polyimide component can be carried outat an ambient temperature or at elevated temperatures to facilitate thedecomposition process and the removal of decomposition products.Preferably the polyimide decomposition process and the removal of thelow molecular weight decomposition product are carried out concurrentlyin a common solvent media. In one embodiment of this invention, thepolyimide decomposition and removal process is carried out at from about50° C. to about 180° C., preferably from about 80° C. to 150° C. Thetime required to fully decompose polyimide and to remove products of thedecomposition process from the article will depend on the shape and thethickness of the article and on process conditions, such as reagentconcentration, agitation rate, temperature and the like, as will berecognized by those skilled in the art. The porous poly(aryl etherketone) articles are then washed with an alcohol, water, or othersuitable solvent, and dried. Thus formed substrates are than utilized toprepare membrane of this invention by superimposing perfluorohydrocarbonlayers on top of the substrate.

The porous PAEK substrates formed from PEEK blends with poly(etherimide) are characterized by a narrow pore size distribution andfrequently exhibit small average pore diameter. The average porediameter can be below 100 nanometers, and frequently is below 20nanometers. The porous PEEK substrates with small pore diameter (100nanometer pore diameter and below) are further characterized by a highspecific surface area. The porous PAEK membranes with pore diameterbelow 100 nm, and surface pores below 20 nm are particularly preferredfor preparation of membrane with porous perfluorohydrocarbon surfacelayers most suited for membrane distillation and liquid degassingapplications. It was found surprisingly that porous composite PAEKmembranes are super-hydrophobic and can be utilized to separate andrecover volatile components from solutions by membrane distillation. Inparticular, ethanol can be removed from water based solutionsselectively. This make composite PAEK membranes of this invention highlysuitable for ethanol recovery from fermentation solutions and forproduction of alcohol free beverages. The composite porous membranes ofthis invention are further highly suited for recovery of butanol fromaceton/butanol/ethanol, ABE, fermentation solutions. The products offermentation can be removed and recovered from the fermentation solutionin a continuous or in a batch process. Considerable reduction in thecost of ethanol butanol production can be attained, when thefermentation process is combined with alcohol extraction from thefermentor. Selective removal of alcohol increases the volumetricproductivity of the fermentor, lowers product inhibition and allowshigher cell density. It is possible to completely convert a much moreconcentrated glucose feed into alcohol when alcohol is removed directlyfrom the fermentor, or by recycling the contents of a continuousfermentor through a separation device which retains cell viability byremoving alcohol. With less water to carry through the process, and lessto remove from the product, the overall cost is reduced.

The composite membrane of this invention can be in the form of a flatsheet film, a tube, a hollow fiber, or any other desirable shape. In thecase of hollow fibers, the fiber preferably possess an outside diameterfrom about 50 to about 5,000 micrometers, more preferably from about 80to about 1,000 micrometers, with a wall thickness from about 10 to about1,000 micrometers, preferably from 20 to 500 micrometers. In the case offilms, the film preferably possess a thickness of from about 10 to about1,000 micrometers, most preferably from about 25 to about 500micrometers. The films may be optionally supported by a permeable clothor a screen.

It is also within the scope of present invention to form in multilayercomposite membranes or membranes with multiple zones that differ in poresize. The multi-zone porous membranes that contain porous zones thatdiffer by at least about 10% in the average pore size or by at leastabout 5% in the pore volume impart certain advantages to mechanical orseparation characteristics of the membrane. For example, the multi-zoneporous membranes can provide unproved mechanical properties, exhibit alower cross membrane pressure drop and exhibit a decreasedsusceptibility to breach in membrane separation layer. The multi-zoneporous membranes are formed from two or more PAEK/porogen blends thatdiffer in blend chemical composition. The blends can, for example,contain different PAEK and polyimide polymer porogen components.Preferably, the chemical composition of individual blends differ in thePAEK/polyimide ratio. The PAEK polymers content of the first blend candiffer from the PAEK polymer content of the second and any additionalblend by at least 1 weight percent, preferably by at lease 5 weightpercent, more preferably by at least 10 weight percent.

The multilayer flat sheet membranes or multilayer membranes of thetubular configuration can contain two, three or more contiguous layersthat differ in the average pore size and/or pore volume. Furthermore,the individual layer can vary from about 1% of the overall membranethickness or less to about 99% of the membrane thickness or more,typically from 10% to 90% or the membrane thickness. The layer comprisedof the smaller average size pores can be about 1 micrometer thick orless to about 100 micrometers thick or more and is supported by orsandwiched between layers with a substantially larger average pore size.

One method of forming composite membranes of this invention is to reactthe preformed PAEK substrate with a perfluorohydrocarbon containing aprimary amino group via formation of ketimine linkages as illustratedbelow:

wherein R is a substituted perfluoro radical, —NH—R′, or a perfluorohydrocarbon substituted ethyl radical, —CH₂—CH₂—R′.Examples of perfluorohydrocarbon radicals R′ include perfluorobutyl, perfluorohexyl,perfluorooctyl, perfluorododecyl, perfluorohextyl, and the like.

To attain optimal surface modification the reaction is preferablycarried out in anhydrous conditions at a temperature between 50° C. to200° C., preferably between 80° C. to 150° C., most preferably between100° C. and 120° C.

Another preferred method of forming composite membranes of thisinvention is by reacting the porous PAEK substrate modified withreactive surface groups with a functional perfluorohydrocarbon. Theperfluorocarbon group modified PAEK membranes can be prepared bymodifying porous PAEK article with an amino-functionalperfluorohydrocarbon as described above or by a two step process whereinthe porous PAEK article is first functionalized and the functionalgroups are then reacted with reactive groups in a functionalperfluorohydrocarbon. For example, the porous PAEK substrate isfunctionalized with hydroxyl groups or ≈C═N—CH₂CH₂OH groups that can bereacted with a perfluorohydrocarbon containing an epoxide group, anisocyanate group or a silane group. Examples of perfluorohydrocarbonscontaining reactive functional groups include FluoroPel PEC 601AFA(containing silane reactive groups) and PFC 504A/coE5 (containingepoxide reactive groups), both commercially available from CytonixCorporation. The surface hydroxyl groups can be formed by reducingketone groups on the surface of PAEK substrate with a reducing reagentsuch as sodium borohydride or by forming ≈C═N—CH₂CH₂OH groups byreacting ketone groups with monoethanolamine.

In another embodiment of this invention the surface of the functionallymodified PAEK substrate can be sequentially further modified byattaching extender groups by reacting with molecules containing one ormore reactive functional groups. Examples of reactive functional groupinclude an epoxide group, an isocyanate group, a silane group or atriazine chloride. A well know isocyanate or trichloro triazine couplingchemistry can be advantageously utilized to conduct the sequentialfunctionalization:

The functional extender groups are then in turn are reacted withfunctional perfluorohydrocarbons to form membranes of present invention.

In one embodiment the preparation of porous PAEK substrate and itssurface modification are carried out simultaneously. Namely, if theporous PAEK article is formed by the RPR process utilizing a primaryamine, the reaction can be carried out under conditions that affect boththe formation of the porous PAEK article and the modification of theporous PAEK article via ketimine group formation in a single stepprocess. Carrying out the RPR process at elevated temperatures,preferably above 80° C., most preferably from about 100° C. to about120° C., in an anhydrous reaction media while utilizing a highconcentration of amine reagent, leads to the formation of a porous andfunctionally modified PAEK substrate in a single step. In one suchexample, porous PEEK substrate modified with ≈C═N—CH₂CH₂OH groups isformed in a single step process from PEEK/PEI blend by reacting theprecursor blend article with neat monoethanolamine at about 120° C.

In some embodiments, it is desirable to form unmodified porous PAEKarticles by the RPR process from PAEK/PI blends. The unmodified PAEKarticle is than functionalized by reacting with a target primary amine.To form an unmodified porous PAEK article by the RPR process theprecursor PAEK/PI blend article is contacted with the primary amineunder conditions that suppress ketimine group formation, i.e. atmoderate temperatures and in a relatively dilute amine solution thatpreferably further contains water. It will be recognized by thoseskilled in the art that by selecting balanced reaction conditions thePAEK modification via formation of imine linkages can be largelysuppressed while an adequately high rate of PI phase decomposition isstill maintained. For example, the RPR process can be carried outmonoethanolamine/dimethylformamide/water mixture 20/70/10 by volume at80° C. that provides for a high rate of porous PAEK article formationwhile suppressing functionalization via the imine group formation. Thepreferred reaction temperature is from about 70° C. to about 100° C.

The unmodified porous PAEK articles prepared as described above can bemodified by reducing surface ketone groups to form hydroxyl groups or byreacting with primary amine reagents to impart target functionality. Themodification can be performed throughout the porous structure or carriedout selectively at the surface of the porous article only. Theapplication requirements determine the mode of the modification and thefunctionality of the modifying agent.

The functionalization process of this invention further provides forpreparation of composite membranes with an ultra-thin graft separationlayer. The process can be carried out under a condition that localizesthe modification to the surface region only. For example, compositemembranes can be formed utilizing preformed porous PAEK substrate bycarrying out the functionalization process under conditions that preventocclusion of the reactant graft molecules into the porous substrate. Theocclusion can be limited by utilizing reactants with a molecular weightwhich is higher than the molecular weight cut-off of the poroussubstrate. Composite membranes with an ultra-thin polymeric layer canthus be formed. Alternatively the graft composite membrane with anultra-thin polymeric layer can be formed by first depositing a thingraft separation layer on top of a dense substrate prepared fromPEEK/PEI blend and then removing the PEI phase in a subsequent step byselectively decomposing and removing PEI polymer to form the poroussub-layer structure. The grafting on top of the dense substrate preventsthe occlusion of the graft layer material into the porous structure andfacilitates the formation of the ultra-thin separation layer. Thefollowing three-step process is thus typically utilized to prepare thegraft composite membrane. First a precursor of a desired shape, such ashollow fiber, is formed form the PEEK/PEI polymer blend by meltprocessing. In the second step, a graft perfluoropolymer separationlayer is formed on top of the precursor. In the third step, the PEIcomponent is removed by decomposing the PEI polymer into low molecularweight, highly soluble fragments by contacting the precursor withaliphatic amine, such as monoethanolamine, thus forming the porousstructure underneath the separation layer. Since the porous structure isdeveloped after the separation layer is formed the occlusion of thesubstrate by the graft molecules is prevented and an ultra-thinseparation layer of graft polymer is formed.

The PAEK membranes of present invention can be also prepared bydepositing a perfluoropolymer layer directly onto unmodified porous PAEKsubstrate or onto PAEK substrate grafted with perfluorohydrocarbons. Theperfluoropolymer layer can be deposited by solution coating or laminatedby molding. Examples of perfluoropolymers useful in preparation of suchcomposite membranes include copolymersof2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (BDD) andtetrafluoroethylene (TFE), fluoro-5-trifluoromethoxy-1,3-dioxide basedpolymer and poly(perfluorobutenyl vinyl ether). It was found thatcomposite membranes with dense ultra-thin defect free separation layerscan be formed by solution coating porous PAEK substrates grafted withperfluorohydrocarbon. The PAEK substrates with surface pore size below20 nm are particularly useful in preparation of composite membranes withdefect free ultra-thin surface layers. The coating layers areessentially non-occlusive and thus exhibit improved gas transportcharacteristics. The coating layers are preferably 0.5 micron thick orless, and most preferably 500 Å thick or less. Ultra-thin defect freelayers can be also formed by coating PAEK substrates containing reactivefunctional groups with a mixture of perfluoropolymer and functionaloligomer. The oligomer reacts with functional groups on the surface ofPAEK substrate and thus improves coating adhesion.

The surface modification and pore size adjustment by grafting can beconveniently carried out without altering PAEK substrate morphologysince the substrate is solvent resistant. The separation characteristicsof the graft membranes, such as molecular weight cut off can be tailoredby employing functional oligomers and polymers of different molecularweight. The separation layers of conventional composite membranes areprone to delamination and the long term, durability and chemicalstability of these membranes in aggressive solvent media is a concern.The perfluorohydrocarbon separation layer of membranes of presentinvention is chemically grafted to the PAEK substrate and thus does notdelaminate and exhibits superior durability in aggressive organicsolvent systems.

The perfluorohydrocarbon modified porous PAEK membranes exhibit lowsurface energy and are thus essentially hydrophobic. Even porousmembrane with relatively large pore size of up to 1 micron do not wetout with water based solutions. These properties make such membranesmost useful for the preparation of porous membranes for gas-liquidtransfer devices in water based systems, i.e. membrane contactors. ThePAEK membranes with pore diameter below 100 nanometer when modified withperfluorohydrocarbon groups exhibit exceptionally high water bubblepoint and do not wet out with alcohols. These properties make suchmembranes most useful for the preparation of porous membranes forgas-liquid transfer devices, i.e. membrane contactors, and as membranedistillation devices. For example, membrane with average pore diameterof 20 nm exhibits water bubble point above 400 psig and is particularlysuited for contactor membranes that process alcohol based feedsolutions. It was found surprisingly that oleophobic PAEK membranes cangenerate concentrated alcohol product from dilute ethanol feed solutionin a single step membrane distillation process. Thus these membranes canbe utilized to recover/remove alcohols such as methanol, ethanol,isopropanol or butanol, from fermentation solutions. The alcohol isrecovered by applying vacuum or a sweep gas to the permeate side of themembranes. The alcohol can be also recovered by absorption into a liquid(strip solution) such as oleic acid or dodecanol. The membranes withdense perfluorohydrocarbon layers do not wet out with hydrocarbons andcan be utilized as membrane contactors for processing hydrocarbonfluids.

The porous poly(aryl ether ketone) based membranes of this invention canbe utilized in numerous fluid separation applications, such asmicrofiltration, nano-filtration, membrane distillation, gasseparations, and as membrane contactors. The fluid separation methodtypically involves contacting a feed fluid with the membrane of thisinvention under conditions that sustain a pressure differential acrossthe membrane (or a partial pressure differential in the case of gascomponents). The pressure differential can be generated be pressurizingfeed fluid, or by applying vacuum or a sweep gas to the permeate side.At least a fraction of the feed mixture is allowed to permeate throughthe membrane and the remaining fraction of the fluid is collected as anon-permeate. In the process of the permeation, the permeate fraction isenriched in a fast permeating component and the non-permeate fraction ofthe feed mixture is depleted in this component. The component orcomponents can be in the form of a solute or gas dissolved in the feedfluid, a gaseous component being a part of a gas mixture, or as a solidmatter suspended in the feed fluid. Further more, the fluid separationmethod can be a counter-current flow process, tangential flow filtrationprocess, a cross flow filtration process or a dead-end filtrationprocess. The membranes of this invention containing a dense ultra-thinperfluoropolymer separation layer can be utilized for gas separationssuch as oxygen/nitrogen separation, natural gas sweetening, forhydrocarbon recovery from air or natural for hydrogen recovery frompetrochemical and refinery streams and gas dehydration applicationsincluding alcohol/water separation. These membranes can be also utilizeds contactor membrane to remove gases from liquids or for controlleddissolution of gases into liquids.

Membranes of this invention that do not wet out with low surface tensionliquids can be utilized as contactors to remove dissolved or suspendedwater from fluids including hydraulic fluid, oils such as thetransformer oil, and diesel fuels, in particular the bio-diesel. Thesecontactor membranes can be further utilized to remove dissolved gasessuch as oxygen from liquids including water based solutions and organicsolvents such as jet fuel.

The present invention is described below by examples, which should notbe construed as limiting the present invention.

EXAMPLES Preparative Example 1

This preparative example describes preparation of porous PEEK substratemodified with hydroxyl groups in a single step pore formation surfacemodification process.

A precursor 25μ thick film was obtained by compression molding PEEK/PEIblend (50:50 by weight pre-blended in a twin extruder) at ca. 370° C.followed by quenching in water. The film was then heat treated at 250°C. for 1 hour to affect crystallization of PEEK polymer. The film wasthen placed into neat monoethanolamine solution maintained at 120° C.for 4 hours. The solution was blanketed with nitrogen. The thus formedporous PEEK film was washed with IPA and then Soxlet extracted withmethanol overnight. The porous film was then dried under vacuum at 80°C. overnight. The elemental analyses indicated that the film contained1.26% of nitrogen. No residual polyimide was detected by FT-IR analyses.The nitrogen presence was attributed to formation of imine groups.

Preparative Example 2

This preparative example describes preparation of porous PEEK substratewithout surface modification.

A precursor film was obtained by compression molding PEEK/PEI bled(50:50 by weight pre-blocked in a twin extruder) at ca. 370° C. followedby quenching in water. The film was then heat treated at 250° C. for 1hour to affect crystallization of PEEK polymer. The film was then placedinto solution comprised of DMF, monoethanolamine and water 90/5/5 byvolume at 100° C. for 4 hours. The solution was blanketed with nitrogen.The thus formed porous PEEK film was washed with IPA and then Soxletextracted with methanol overnight. The porous film was then dried undervacuum at 80° C. overnight. The elemental analyses indicated that thefilm contained 0.09% of nitrogen. No residual polyimide was detected byFT-IR analyses. The results indicate that thus obtained porous PEEKsubstrate is essentially free of surface modification via imine groupformation.

Preparation Example 3

This preparative example demonstrates preparation of PEEK substratefunctionalized with hydroxyl groups by selective reduction of surfaceketone groups.

A porous PEEK film prepared as described in Preparative Example 2 waspre-dried under vacuum at 100° C. overnight. The pre-dried film was thenplaced into a 0.1% sodium borohydride solution in isopropyl alcohol andrefluxed for 8 hours. The film was then washed sequentially with diluteHCl solution (0.1 N) and distilled water and then dried under vacuum at80° C. to a constant weight. The thus obtained film was found to behighly hydrophilic and spontaneously wetted with water.

Example 4

This example demonstrates preparation of super-hydrophobic membranes ofthis invention by surface grafting.

A porous PEEK film prepared as described in Preparative Example 1 thatcontained surface hydroxyl groups was first dried under vacuum at 100°C. overnight. The pre-dried film was then dipped into 1% solution offunctional perfluorohydrocarbon PFC 504A/COE5 obtained from CytonixCorporation. The dip coated porous membrane was air dried followed byheat treatment at 90° C. for 2 hours. The thus obtained porous membranewas found to be highly hydrophobic and did not wet out by isopropanol atroom temperature. The membrane exhibited high gas permeance (Hepermeance 5400 GPU) and He/N₂ separation factor of 2.6. {GPU=1×10⁻⁶ cm³(STP)/cm²·s·cmHg}.

Example 5

This example demonstrates preparation of super-hydrophobic membranes ofthis invention by modifying PEEK substrate first with hydroxyl groupsfollowed by surface grafting with perfluorohydrocarbons.

A porous PEEK substrate film that contained hydroxyl surface groupsformed by selective ketone group reduction was prepared as described inPreparative Example 3. The film was pre-dried under vacuum at 100° C.overnight. The pre-dried film was then dipped into the 1% solution offunctional perfluorohydrocarbon EEC 504A/COE5 obtained from CytonixCorporation. The coated porous membrane was air dried and then furtherheat treated at 90° C. for 2 hours. The thus obtained porous membranewas found to be highly hydrophobic and did not wet out by isopropanol atroom temperature. The membrane exhibited high gas permeance (Hepermeance 5600 GPU) and He/N₂ separation factor of 2.6. {GPU=1×10⁻⁶ cm³(STP)/cm²·s·cmHg}.

This example demonstrates preparation of composite superhydrophobicmembrane of present invention.

A precursor PEEK hollow fiber was obtained by melt extrusion of PEEK/PEIblend (50:50, by weight). The precursor hollow fiber had 16 mil outsidediameter and 11 mil inside diameter. The hollow fiber was heat treatedat 250° C. for 1 hour and then placed for 8 hours into monoethanolaminemaintained at 100° C. The porous hollow fiber was washed with IPA andthen with water. The porous hollow fiber was dried at 80° C. undervacuum overnight. The hollow fiber was then treated with 1% solution ofPFC 504A/COE5. The treated hollow fiber was then subjected to heattreatment at 90° C. for 2 hours. The thus prepared porous hydrophobichollow fiber was further dip coated with 1% solution of Hyflon AD60polymer dissolved in PF589 perfluorinated solvent obtained from Solvayand 3M Corporations, respectively. The composite membrane prepared bythis process was highly hydrophobic and did not wet out by cyclohexane.The membrane exhibited high oxygen permeance of 190 GPU anoxygen/nitrogen separation factor of 2.9.

Example 7

This example demonstrates selective recovery of ethanol fromethanol/water solutions by the super-hydrophobic membrane of thisinvention.

A precursor PEEK hollow fiber was obtained by melt extrusion of PEEK/PEIblend (50:50, by weight). The precursor hollow fiber had 16 mil outsidediameter and 11 mil inside diameter. The hollow fiber was heat treatedat 250° C. for 1 hour and then placed for 8 hours into monoethanolaminemaintained at 100° C. The thus formed porous hollow fiber was washedwith IPA and then with water. The porous hollow fiber was dried at 80°C. under vacuum overnight. The hollow fiber was then treated with 1%solution of PEC 504A/COE5. The treated hollow fiber was then subjectedto heat treatment at 90° C. for 2 hours. The thus obtained hydrophobichollow fiber membrane was utilized to separate ethanol from water.

The ethanol/water separation was carried out utilizing hollow fibermodule equipped with hydrophobic hollow fibers. The module was 14 inchlong and contained about 30 hollow fibers. The feed solution (10%ethanol/water by weight) was circulated through the shell side of thehollow fiber module and the permeate vapor was collected on the boreside of the membrane by condensing in a dry ice trap. The driving forcewas generated by applying vacuum on the permeate side (the vacuum wasmaintained at about 0.2 atm). The ethanol concentration in the permeatewas measured by the refractive index and the membrane flux was measuredgravimetrically based on the weight of the liquid collected. Themembrane exhibited ethanol flux of 0.05 kg/m² hour and ethanol/waterseparation factor of 80 at room temperature. The separation factor (α)of ethanol relative to water is defined as the ratio of permeatecompositions divided by the ratio of the feed compositions as follows:

$\alpha_{{ethanol}/{water}} = \frac{\left( {C_{ethanol}^{P}/C_{water}^{p}} \right)}{\left( {C_{ethanol}^{f}/C_{water}^{f}} \right)}$

Wherein C_(ethanol) ^(p) is the ethanol concentration in the permeate,C_(water) ^(p) is the water concentration in C_(ethanol) ^(f) thepermeate, is the ethanol concentration in the feed, and C_(water) ^(f)is the water concentration in the feed.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A process for preparing a composite membrane, theprocess comprising: a. forming a blend of poly(aryl ether ketone)polymer with a polyimide; b. shaping the blend to form a shapedsubstrate; c. optionally annealing the shaped substrate; d. bringing theshaped substrate into contact with a primary amine to decompose thepolyimide into low molecular weight fragments while functionalizing thepoly(aryl ether ketone) with the primary amine; e. removing the lowmolecular weight fragments from the substrate to form a porous poly(arylether ketone); f. washing the porous poly(aryl ether ketone) substrate;g. drying the porous poly(aryl ether ketone) substrate; and h. graftingthe porous poly(aryl ether ketone) substrate with aperfluorohydrocarbon, thereby forming the composite membrane.